Re: Do all the legs of an "OR" with null comparisons get executed?
Date: Mon, 31 Mar 2008 05:46:20 -0700 (PDT)
Message-ID: <87698f09-25e3-45ce-a60d-6fe90fef85f7@u69g2000hse.googlegroups.com>
On Mar 30, 5:59 pm, Arthernan <arther..._at_hotmail.com> wrote:
> On Mar 29, 12:43 pm, Charles Hooper <hooperc2..._at_yahoo.com> wrote:
> > On Mar 28, 5:43 pm, Arthernan <arther..._at_hotmail.com> wrote:
>
> > > If I do an explain plan of the statement below I can see that the
> > > "and" clauses that have MMDDOB=NULL do not get executed
>
> > > select * from v_search where
> > > UPP_FIRST='JOHN' and UPP_LAST='SMITH' and MMDDOB=NULL and AA=1 or
> > > UPP_FIRST='JOHN' and UPP_LAST='SMITH' and BB=2 or
> > > UPP_FIRST='JOHN' and UPP_LAST='SMITH' and CC='CA' or
> > > UPP_FIRST='JOHN' and MMDDOB=NULL and AA=1 and BB=2 or
> > > UPP_FIRST='JOHN' and MMDDOB=NULL and AA=1 and CC='CA' or
> > > UPP_FIRST='JOHN' and BB=2 and CC='CA' or
> > > UPP_LAST='SMITH' and MMDDOB=NULL and AA=1 and BB=2 or
> > > UPP_LAST='SMITH' and MMDDOB=NULL and AA=1 and CC='CA' or
> > > UPP_LAST='SMITH' and BB=2 and CC='CA' or
> > > MMDDOB=NULL and AA=1 and BB=2 and CC='CA'
>
> > > My problem is how to know if it does the same thing when I parametize
> > > the query as
>
> > > select * from v_search where
> > > UPP_FIRST=:UPP_FIRST and UPP_LAST=:UPP_LAST and MMDDOB=:MMDD and
> > > AA=:AA or
> > > UPP_FIRST=:UPP_FIRST and UPP_LAST=:UPP_LAST and BB=:BB or
> > > UPP_FIRST=:UPP_FIRST and UPP_LAST=:UPP_LAST and CC=:CC or
> > > UPP_FIRST=:UPP_FIRST and MMDDOB=:MMDD and AA=:AA and BB=:BB or
> > > UPP_FIRST=:UPP_FIRST and MMDDOB=:MMDD and AA=:AA and CC=:CC or
> > > UPP_FIRST=:UPP_FIRST and BB=:BB and CC=:CC or
> > > UPP_LAST=:UPP_LAST and MMDDOB=:MMDD and AA=:AA and BB=:BB or
> > > UPP_LAST=:UPP_LAST and MMDDOB=:MMDD and AA=:AA and CC=:CC or
> > > UPP_LAST=:UPP_LAST and BB=:BB and CC=:CC or
> > > MMDDOB=:MMDD and AA=:AA and BB=:BB and CC=:CC
>
> > > On Mar 28, 2:15 pm, Frank van Bortel <frank.van.bor..._at_gmail.com>
> > > wrote:
>
> > > > Arthernan wrote:
> > > > > That is an alternative. I do think the logic is correct thought. Take
> > > > > the first comparison for example:
>
> > > > > UPP_FIRST='JOHN' and UPP_LAST='SMITH' and MMDDOB=NULL and AA=1
>
> > > > MMDDOB=NULL should be "MMDDOB is NULL"
>
> > > > And no, Oracle is smart enough to know boolean algebra; if
> > > > a part of the boolean equation yields true (or false), the
> > > > rest is no executed - it would not change the outcome.
>
> > > > Now, you figure out when to OR or AND, and when TRUE or
> > > > FALSE :)
> > > > --
>
> > > > Regards,
> > > > Frank van Bortel
>
> > > > Top-posting in UseNet newsgroups is one way to shut me up
>
> > > But if I did "MMDDOB is NULL" instead of MMDDOB=NULL. I would get
> > > records back when I don't want them.
>
> > > The final query will be parametized like this "MMDDOB=:MMDDOB". So I
> > > want to know if :MMDDOB happens to be NULL, will oracle be smart
> > > enougth to realize that whole "and clause" can go away. For example if
> > > I did MMDDOB=1231, whenever MMDDOB was NULL the row would be filtered
> > > out. Just look at my original SQL above and you will see what I mean.
>
> > > Arturo Hernandez- Hide quoted text -
>
> > > - Show quoted text -
>
> > Look closely at the responses that Frank van Bortel provided to you.
> > The WHERE clause is not working the way you expect, and that is why
> > you receive too many rows when using MMDDOB IS NULL.
>
> > Placing ( ) as Oracle would evaluate the WHERE clause:
> > (((((((((((((((((((((((((((((((((((UPP_FIRST='JOHN' and
> > UPP_LAST='SMITH') and MMDDOB=NULL) and AA=1) or {UPP_FIRST='JOHN') and
> > UPP_LAST='SMITH') and BB=2)} or UPP_FIRST='JOHN') and
> > UPP_LAST='SMITH') and CC='CA') or UPP_FIRST='JOHN') and MMDDOB=NULL)
> > and AA=1) and BB=2) or UPP_FIRST='JOHN') and MMDDOB=NULL) and AA=1)
> > and CC='CA') or {UPP_FIRST='JOHN') and BB=2) and CC='CA')} or
> > UPP_LAST='SMITH') and MMDDOB=NULL) and AA=1) and BB=2) or
> > UPP_LAST='SMITH') and MMDDOB=NULL) and AA=1) and CC='CA') or
> > UPP_LAST='SMITH') and BB=2) and CC='CA') or MMDDOB=NULL) and AA=1) and
> > BB=2) and CC='CA')
>
> > Now, let's just replace MMDDOB=NULL with FALSE, as it can never be
> > TRUE (as indicated by several people in this thread):
> > (((((((((((((((((((((((((((((((((((UPP_FIRST='JOHN' and
> > UPP_LAST='SMITH') and FALSE) and AA=1) or {UPP_FIRST='JOHN') and
> > UPP_LAST='SMITH') and BB=2)} or UPP_FIRST='JOHN') and
> > UPP_LAST='SMITH') and CC='CA') or UPP_FIRST='JOHN') and FALSE) and
> > AA=1) and BB=2) or UPP_FIRST='JOHN') and FALSE) and AA=1) and CC='CA')
> > or {UPP_FIRST='JOHN') and BB=2) and CC='CA')} or UPP_LAST='SMITH') and
> > FALSE) and AA=1) and BB=2) or UPP_LAST='SMITH') and FALSE) and AA=1)
> > and CC='CA') or UPP_LAST='SMITH') and BB=2) and CC='CA') or FALSE) and
> > AA=1) and BB=2) and CC='CA')
>
> > Now, let's go through the WHERE clause and set all other conditions to
> > TRUE, just to see what happens if those conditions were TRUE:
> > (((((((((((((((((((((((((((((((((((TRUE and TRUE) and FALSE) and TRUE)
> > or TRUE) and TRUE) and TRUE) or {TRUE) and TRUE) and TRUE)} or TRUE)
> > and FALSE) and TRUE) and TRUE) or TRUE) and FALSE) and TRUE) and TRUE)
> > or TRUE) and TRUE) and TRUE) or TRUE) and FALSE) and TRUE) and TRUE)
> > or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and TRUE) and TRUE)
> > or FALSE) and TRUE) and TRUE) and TRUE)
>
> > In the above, look closely for the curly brackets { } (I did not
> > identify all such cases). Now, simplifying the above a little, we
> > start to see the problem - most of the WHERE clause evaluates to FALSE
> > - always
> > ((((((((((((((((((((((((((((((FALSE or TRUE) and TRUE) and TRUE) or
> > TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and FALSE) and TRUE) and
> > TRUE) or TRUE) and TRUE) and TRUE) or TRUE) and FALSE) and TRUE) and
> > TRUE) or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and TRUE) and
> > TRUE) or FALSE) and TRUE) and TRUE) and TRUE)
>
> > Simplifying again
> > (((((((((((((((((((((((((((TRUE) or TRUE) and FALSE) and TRUE) and
> > TRUE) or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and TRUE) and
> > TRUE) or TRUE) and FALSE) and TRUE) and TRUE) or TRUE) and FALSE) and
> > TRUE) and TRUE) or TRUE) and TRUE) and TRUE) or FALSE) and TRUE) and
> > TRUE) and TRUE)
>
> > There are only a couple of conditions in the above that could possibly
> > evaluate to TRUE.
>
> > The reason that the WHERE clause does not work with the MMDDOB IS NULL
> > condition is due to the order of evaluation. You did not specify the
> > evaluation order by using ( ) in the WHERE clause, so Oracle used the
> > default (note that the default evaluation order differs from some
> > programming languages, such as C).
>
> > Charles Hooper
> > IT Manager/Oracle DBA
> > K&M Machine-Fabricating, Inc.
>
> I really appreciate your time, but I do not think my question is
> coming throught. I am going to parametize my query. So I am not really
> going to execute something that reads .... A=NULL... What I am going
> to have is ..... A=:A....notice the colon before the second A. I do
> not know if :A will have a NULL value. Just like I don't know if A
> will have one a NULL value. I understand Oracle execution enough to
> know the logic matches the intent. What I do not know is how will it
> be executed.
Let's test. Here is the setup for the test run:
CREATE TABLE T1(
UPP_FIRST VARCHAR2(6),
UPP_LAST VARCHAR2(6),
MMDDOB DATE,
AA NUMBER(5),
BB NUMBER(5));
INSERT INTO T1 VALUES(
'JOHN',
'SMITH',
NULL,
1,
NULL);
INSERT INTO T1 VALUES(
'JOHN',
'SMITH',
TO_DATE('01012008','MMDDYYYY'),
1,
NULL);
INSERT INTO T1 VALUES(
'JOHN',
'SMITH',
NULL,
1,
2);
INSERT INTO T1 VALUES(
'JOHN',
'SMITH',
TO_DATE('01012008','MMDDYYYY'),
1,
2);
COMMIT;
SELECT
*
FROM
T1;
UPP_FI UPP_LA MMDDOB AA BB ------ ------ --------- ---------- ----------
JOHN SMITH 1 JOHN SMITH 01-JAN-08 1 JOHN SMITH 1 2 JOHN SMITH 01-JAN-08 1 2
We have 4 rows in the table, two with a value for MMDDOB, and two with
a value for BB. Now, a simple select using the first two criteria
that you specified in the SQL statement that you posted:
SELECT
*
FROM
T1
WHERE
UPP_FIRST='JOHN' and UPP_LAST='SMITH' and MMDDOB=NULL and AA=1
or UPP_FIRST='JOHN' and UPP_LAST='SMITH' and BB=2;
You want 3 rows to be returned, but Oracle returns: UPP_FI UPP_LA MMDDOB AA BB ------ ------ --------- ---------- ----------
JOHN SMITH 1 2 JOHN SMITH 01-JAN-08 1 2
Now, what happens when we switch to using bind variables, do we see the third row in the result? A simple VB program using ADO to find out:
Dim comData As ADODB.Command
Dim snpData As ADODB.Recordset
Dim strSQL As String
Dim intRows As Integer
Set comData = New ADODB.Command
Set snpData = New ADODB.Recordset
strSQL = "SELECT" & vbCrLf
strSQL = strSQL & " *" & vbCrLf
strSQL = strSQL & "FROM" & vbCrLf
strSQL = strSQL & " T1" & vbCrLf
strSQL = strSQL & "WHERE" & vbCrLf
strSQL = strSQL & " UPP_FIRST= ? and UPP_LAST= ? and MMDDOB= ?
and AA= ?" & vbCrLf
strSQL = strSQL & " or UPP_FIRST= ? and UPP_LAST= ? and BB= ?"
With comData
'Set up the command properties
.CommandText = strSQL
.CommandType = adCmdText
.CommandTimeout = 30
.ActiveConnection = dbMyDB
'Add the bind variables
.Parameters.Append .CreateParameter("first1", adVarChar,
adParamInput, 6, "JOHN")
.Parameters.Append .CreateParameter("last1", adVarChar,
adParamInput, 6, "SMITH")
.Parameters.Append .CreateParameter("dob1", adDate,
adParamInput, 8, Null)
.Parameters.Append .CreateParameter("aa", adNumeric,
adParamInput, 8, 1)
.Parameters.Append .CreateParameter("first2", adVarChar,
adParamInput, 6, "JOHN")
.Parameters.Append .CreateParameter("last2", adVarChar,
adParamInput, 6, "SMITH")
.Parameters.Append .CreateParameter("bb", adNumeric,
adParamInput, 8, 2)
End With
Set snpData = comData.Execute
intRows = 0
Do While Not (snpData.EOF)
intRows = intRows + 1
snpData.MoveNext
Loop
Debug.Print "Rows Retrieved "; intRows
The output is: Rows Retrieved 2 {the same result as our SQL query}
If we change the third parameter as follows: .Parameters.Append .CreateParameter("dob1", adDate, adParamInput, 8, CDate("01/01/2008"))
The output is Rows Retrieved 3 {the number of rows that were expected}
If we reset the third parameter back to NULL and also specify the last
parameter (bb) as NULL:
.Parameters.Append .CreateParameter("first1", adVarChar,
adParamInput, 6, "JOHN")
.Parameters.Append .CreateParameter("last1", adVarChar,
adParamInput, 6, "SMITH")
.Parameters.Append .CreateParameter("dob1", adDate, adParamInput, 8,
Null)
.Parameters.Append .CreateParameter("aa", adNumeric, adParamInput,
8, 1)
.Parameters.Append .CreateParameter("first2", adVarChar,
adParamInput, 6, "JOHN")
.Parameters.Append .CreateParameter("last2", adVarChar,
adParamInput, 6, "SMITH")
.Parameters.Append .CreateParameter("bb", adNumeric, adParamInput,
8, Null)
The output is:
Rows Retrieved 0 {MMDDOB=NULL OR BB=NULL returns 0 rows}
I recognize that not everyone programs in VB, but perhaps someone will post a simple example using bind variables in another language.
Charles Hooper
IT Manager/Oracle DBA
K&M Machine-Fabricating, Inc.
Received on Mon Mar 31 2008 - 07:46:20 CDT